Polymer solutions viscosity

There are some limitations to this technique. First, proper mixing can only be achieved with dilute, low viscosity polymer solutions (perhaps a few percent polymer by mass), so the final films are at most a few hundred nanometers thick. This can be a problem if confinement will create undesired effects in the blend behavior. 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

I he diagram of Fig. 9-1 is typical of mixtures of two small molecules, or of two polymers of comparable molecular weight and comparable viscosity. Polymer solutions, or blends of two polymers with very different molecular weights, have asymmetric phase diagrams, reflecting the asymmetry of the molecular sizes (see Fig. 9-2). 

The most widely applied preparation method is dipping the supports in a polymeric solution. To remove excess polymer efficiently from the channels, low-viscosity polymer solutions are preferred as carbon precursors. The most straightforward method is the dipcoating method [6] The honeycombs are dipped in a precursor solution and then dried and/or cured. Subsequently, the precursor is carbonized and, if needed, activated. Many different carbon precursors have been nsed, such as saccharides [1,8], polyfurfuryl alcohol (PFA) [5,9], and phenohc... 

Madabhushi, R.S., Separation of 4-color DNA sequencing extension products in noncovalently coated capillaries using low viscosity polymer solutions. Electrophoresis, 19, 224, 1998. 

Under polymer synthesis there is considerable number of processes proceeding under phase separation conditions, in particular in such systems like "liquid-liquid" (high-viscosity polymer solution - low-molecular fluid), "gas-liguid" (polymer-analogous processes) and "solid-liquid" (catalytic polymerization). Necessity of substance transfer from one phase to another by mass-exchange [140], i.e. removal of diffusive limitations is the feature of heterogeneous processes. In this case one have to deal with serious problems while realizing fast chemical reactions [141]. 

High-viscosity gels (e.g., the high-Mw LPA) require either in situ polymerization or very high pressure to replace them in the capillary. In contrast, many of the low-viscosity polymer solutions do not require polymerization by the user. It is necessary only to dissolve a known amount of the polymer in basic buffers, such as tris-borate-EDTA (TBE) or 3-[[tris(hydroxymethyl)methyl]amino] propane-sulfonic acid (TAPS) (pH 8-9), or isoelectric buffers, such as His or Lys. Because the low conductivity of the isoelectric buffers minimizes Joule heating, high electric fields can be used for rapid separation. For oligonucleo-... 

This article discusses polymerization reactors where the continuous phase is a solution of a polymer in its own monomer or in a solvent. When the low molecular weight species is primarily monomer, the reaction is a bulk polymerization and when it is a solvent, the reaction is a solution polymerization. This distinction has little practical importance. The important consideration is that a high viscosity polymer solution is the continuous phase and is in contact with the reactor walls and the agitator. In contrast, suspended-phase polymerizations (such as emulsion, dispersion, and suspension) and gas-phase polsrmerizations have a low viscosity continuous phase (see Heterophase Polymerization). 

The linear polymer can be prepared either from a difunctional N-cyanourea monomer or directly from the mixture of a diisocyanate and cyanamide having a 1 to 2 mole feed ratio in a solvent such as N-methyl pyrrolidone at room temperature. The viscosity of the polymerization mixture increased with time and finally turned to gel upon stirring at room temperature. A high molecular weight polymer was obtained by adding the highly viscosity polymer solution to a large quantity of acetone after 72 hours of polymerization. For example, a fluffy white polymer was obtained from the polymerization of di(p-isocyanato-phenyl) methane and cyanamide at room temperature. 

Very thin CNT-polymer composite films (thickness % 200 nm) can be produced by means of spin casting in which suspensions of CNTs in low viscosity polymer solutions are deposited drop wise to the center of a rotating substrate [118]. Spiiming for 20-30 sec at 3,000 rpm has been reported to produce electron-transparent films. The centrifugal forces induce radial flow of the drop resulting in thin films with some preferred orientation of the embedded CNTs along the direction of flow. Fabrication of continuous CNT-polymer composite films has been demonstrated by extrusion of CNT composite thermoplastic through a slit die followed by take-up onto a chilled roller [119-120]. 

Tuladhar, T. R., Mackley, M. R. (2008). Filament stretching rheometry and break-up behaviour of low viscosity polymer solutions and inkjet fluids. Journal of Non-Newtonian Fluid Mechanics, 745(1-3), 97-108. 

Flood response was quicker than expected and shows a slower rate of incremental recovery than the model prediction. This is probably due to the injection of lower viscosity polymer solution than the design called for, lack of a gravity component in the simulations, and rock and saturation variations in the reservoir. 

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